Resistance welder



D. M. DUINKER ETAL RESISTANCE WELDER Dec. 17, 1940.

Filed Nov. 24, 1957 Patented Dec. 17, 1940 UNITED STATES PATENT OFFICE RE SISTANCE WEIDER Application November 24, 1937, Serial No. 176,344 In Germany December 14, 1936 2 Claims.

Our invention relates to resistance Welders which are operated from alternating current mains, and more particularly, to automaticallytimed Welders.

With such Welders it is necessary that the 5 welding current-Which frequently amounts to several thousand amperes-lows through the material being welded for short and preferably variable time periods and at regular time intervals. As mechanically-operated switches are not entirely satisfactory for this purpose, the timing is generally effected by means of a grid-controlled, gas-filled tube having either an incandescent or mercury cathode, i. e., a relay tube.

It has been proposed to control spot-seam Welders by means of an alternating potential which has a variable frequency and ls produced by a separate device. However, We have found that in practice such control devices have the disadvantage that variation o1' the duration of the welding-current impulses also introduces a variation in the duration of the currentless time intervals, i. e., the period between the welds.

The object of our invention is to overcome the above difculties, and to provide a Welder which may be used for either spot or spot-seam Welding and in which the time of the duration of the current impulses and the currentless intervals can be varied independently of each other.

In accordance with the invention we control the duration of the current impulses and the duration of the currentless periods by similar arrangements, each of which comprises a retarding chain consisting of at least one condenser and a resistance which controls the conductivity of the discharge path of a gaseous-filled discharge tube, preferably a grid-controlled tube. We so arrange these chain arrangements that the duration of the current impulses and the duration of the currentless periods can be adjusted independently of each other.

The arrangement is preferably such that the condensers o1 the retarding chains when in their charged condition block the auxiliary discharge path or paths, and are charged either indirectly or directly by the Welding current or by a current corresponding thereto.

We are aware that it has been proposed to control the duration of welding-current impulses by inserting a condenser, which hasbeen stepwise charged through a rectifier, in the grid circuit of a gaseous-filled discharge tube, whereby the grid will receive after a controllable time such a negative voltage that the discharge path of the tube becomes non-conductive. However, in

(Cl. Z50- 27) an arrangement according to the invention, the time of the welding-current impulse is determined by a condenser which is connected between the grid and cathode of an auxiliary discharge path and is charged by a second condenser through a preferably variable resistance, whereby the negative bias of a control grid of the auxiliary discharge tube associated with the irst condenser gradually increases to such an extent that after a certain time the discharge path becomes non-conductive; the second condenser being charged through a rectifier as soon as a Welding current iiows.

In accordance with one embodiment of the invention, we use an auxiliary discharge tube having, for instance, two grids, and apply to one of these grids a negative voltage which blocks the discharge path, and so arrange the circuits that the entire apparatus becomes inoperative upon applying this negative voltage.

In order that the invention may be clearly understood and readily carried into effect, we shall describe the same in more detail with reference to the accompanying drawing yin which the single gure is a circuit diagram of a Welder according to the invention. The Welder illustrated may be used for either spot or for spotseam welding, and is provided with a two-pole double-throw switch 21 for this purpose. When switch 21 is in lposition A as shown, the ap` paratus is adapted for spot Welding, and When it is in its second position B the apparatus is adapted for spot-seam welding.

In the ligure, reference numeral I indicates an t object to be Welded which is connected across a secondary winding 30 of a step-down transform-er 2 having a primary winding 3|. Winding 3| has one end connected to one terminal of an alternating current source 3, which may be the .ordinary supply mains, land its other end connected to the other terminal of source 3 through a secondary winding 32 of a coupling transformer 4 having a primary winding 33.

Winding 33 is connected in the plate circuit of a grid-controlled discharge tube 5 having a grid circuit including a biasing battery 35, a Winding 36, and a resistance 34. When tube 5 is non-conductive, the eective impedance of winding 32 is very high, and only a small current can flow through winding 3|, and as a result therewill be no elective flow of welding current in Winding 30. However, when tube 5 is conductive the eiective impedance of winding 32 becomes Very small or disappears entirely, and the current through 'Iibe 6 has a plate circuit including a. secondlo ary winding 39 of a'transformer II whose primary winding 38 is connected across source 3,a winding 31 forming part of a transformer I 5 which also comprises the winding 38. rThe gridV of tube is normally suflicientlynegatively biased by battery 35 so that the current will not ow through winding 33. However, when an alternating current yilows in the plate circuit of 'tube 1 6, an alternating voltage will be inducedin the grid circuit of ,tube 5 to thereby make-.this tube conductive. y

. To controllthe momentat whichthe welding current willfistartto oW, grid r'I is ,connected througha. source of potential9, shown as a transformer, conductor l4 I, .resistance I3, biasing battery AI2and11.conductor 42, ,to cathode I9, 4to

thereby form agrid circuit. Source 9 has a frequencycorresponding to that of source 3 and preferably has a sharp :curve shape to ensure thatthestarting of thefdischarge device takes place at exactly thesame moment o1' every cycle and will.v not Avarynwith voltage variations of source v3 or, temperature changes and `accordingly varying gas pressure ofthe discharge devices. potentiahmaybe obtained/from source 3 through aphase-shifter 51, for instance a react- 'ancey coil withapmovablecore, which serves to vary .the phaseof the Voltageof source 9. Battery l2 negatively biases grid 1 to such an extent that tube 8 isblocked and source 9 does not affect o the plate current vof .this tube.V f

Whenit is Adesiredto weld, a two-pole double- `throw switchv I4 is used. "Switch I4 has two arms 43 and.44,-and can be placed in two positions,fC and D. By placing the switch in position D arm 45 44completesga'shunt circuit across resistance I3 anda vmirtiomof. battery L2, whereby the grid bias g of tube ,l is reduced to such a, degree that thistube becomes conductive upon the occurrence of 'a'. voltagepeak of source i9.,* The moment at 60 which peak"A occurs is determined bythe relationmbetweenthe phases ofthe voltages of source rSand source'3and by varying this phase relation themoment df each l'half 'cycleinwhich current ow through the plate current of tube G'can D,`aseries`of'current impulses takes place in the plate'circuit of tube `6, and this in turn induces in'jtlie grid circ'uitof tube 5 a voltage which makes vthis tube intermittently conductive, As Va'result 'awelding'current' will flow whose intensity can be.

^ controlled by'varying the phase of source 9.

` interrupt this current after a certaintime period of regulable length,"we provide means to control tube 5 `by means of grids.r vFor this pur- 85 pose, We connect between grid 8 and cathode I8, agrid circuitjcomprising Va. condenser I8 and a rectier I1 lconnectedin series acrossa winding `I8 providedon transformer I5. Thefrst'imlpulseofl current at the beginningvof the welding 70 cycle produce a current in winding I6, 'which current after being rectified will charge condenser Y. I9. During the welding condenser I8 chargeslavariable condenser I9 through a variable resistance 29,.. Condenser I9 has one end `15 connectedto cathode I0 and itsother end connected through a limiting resistance'l to grid 8 in such amanner that as the voltage of this condenser becomes higher, grid 8 becomes more negatively biased. By varying the'capacity of condenser I9 and the resistance of resistance 20, 5 it is possible to determine the ytime required for condenser I9 to be chargedto` Aavoltage which Will`s'uilciently bias grid 8 to blockftube 6 and thus the duration of ow of welding current,

Whenswitch I4 is placedin position C,'con 10 densers I8-V and I9 are discharged through a cir- "cuit including conductor 42, arm 43, and a resistance 4 5; the discharging of condenser I9 beying` facilitated byfna rectier 23 connected across resistance,21).v `Asarrn 44 is open, grid 1 is nega- 15 tively biased and tube 6 remainsr blocked.

If the d eviceis now to be usedfor spot-seam welding, switch 21 is placed in position B, whereby a regular series of current impulses is produced, and the duration of the lcurrentless time inter- 20 valsicanbeadjusted independently of the duration of these irnpulsesffI vSuch independent control is very advantageous particularlywhen welding objects of different shape from the same material. chain for determining theduration of currentless time intervals operates v-in a similar manner to the other retarding chain. j

For the rabove purpose, awinding 22 provided on transformer I 5 has one end connected through 30 a conductor y46 to one terminal of a variable con- 'y denser 24 `whose other terminal is connected through conductors 41 and 48, and a-rectier 23 to the other end of the winding 22.` Thus'condenser 241s charged to its full/extent vduring the 35 whole weldin'gperiod. -r

Condenser 24*l has one terminal connected through a limiting resistance 49 to ya grid 5I 'of a discharge tube 26, preferably having a. screengrid 52, and hasits yother terminal connected, through conductorg41 to thefcathode of this tube to therebyv impress such a negative voltage on grid 5|-asto make tube 26 non-conductiye.- Condenser 24 isshunted jby a [variable resistance 25 whereby tube Z5-will become conductive again 45 af-ter a predetermined time and short-circuit corrdensers I8'and I9.vr f 1 I For this purpose, condenser I8 is connected in the plate circuit of tube 25; which circuit may be traced from the plate of this tube through a 50 conductor 53,*a winding 50 of transformer 29, a conductor` 54, armf'of yswitch 21, conductor 56, condenser I8, and conductor 48 to the cathode of `tube 26. condenser I9 in series with the rectifier 28 is shunted across condenser I8, it 55 `Willdischarge in `a. similar manner.. n 1 To insure complete discharge of condenser I8 the primary'winding of transformer 29, is connected to the source'3.

After condensers I 8 andr I9 have been dis- 80 rcharged'in the above. manner through tube 26,

tube- Ii` mfay'again be ignited, whereby. a new cycle begins. 4`

While we have describedour invention with reference to `specific examples and applications, We do rnot .wish yto beV limited theretobut desire the append-ed claims tobe construed as broadly This circuitfarrangement-of the retarding 2.5

denser comprising a resistance, a second condenser connected across said rstkcondenser with the interposition of said resistance, and means to charge said second condenser to always the same polarity with direc'tl current when curreni'I oWs in the load circuit.

2. In a control device in which a load current is vcontrolled by a gaseous discharge tube having a control electrode, means for applying a l!" blocking voltage to said electrode comprising a condenser, a charging circuit for said condenser including a resistance and a second condenser, and means for charging said second condenser to always the same polarity, said means comprising a charging circuit including a rectifier and a supply source, said supply source being effective upon the flow of the load current. 

